Gerwalk mode. And it's the only 1/60 v2 (have almost 30) that has yellowed. It's not the biceps, it's the shoulder pieces (not the shoulder armor) that are made from a different plastic, POM I guess, and those pieces haven't yellowed at all. The white painted parts suffered no discoloration either.
It was displayed on top of a shelf in my new house, and before I installed some blinders there was some sun reflection from a window during the mornings. That must have caused the nasty yellowing. I moved it to a dark room but the yellowing continued. It's some sort of reaction after being exposed to UV light I guess.
Yes, it was displayed in gerwalk mode.
Yeah that sounds easier